WASHINGTON -- "Isenberg! How old are you?"

"I'm old enough to work here," the 19-year-old says.

Although no one under 21 can be hired as a guard in Maryland's state prisons, county jails are permitted to hire correctional officers as young as 18. The more lax requirement makes meeting hiring goals easier, but many corrections officials say young jailers require close supervision and sometimes lack the life experience necessary to manage manipulative inmates.

"I think all of us would rather have them be 21," said Pamela Dottellis, corrections director for Charles County. "It is a big adjustment when those doors slam and inmates are yelling at you or looking over at you."

Dozens of guards under 21 work in jails across Washington's Maryland suburbs and elsewhere in the state. Isenberg is among five such officers in Charles, said Capt. Morris Gant, who manages the 146 correctional officers there.

Aside from his crisp uniform, Isenberg hardly looks the part. He's an inch shy of six feet tall and weighs less than 160 pounds.

A little more than two years ago, he was a senior at Leonardtown High School in St. Mary's County. He enjoyed computers and video games. He was always interested in law enforcement, he said, and he saw a stint as a correctional officer as a good steppingstone to becoming a sheriff's deputy -- a job with a minimum age of 21. He also liked the money in corrections; he started out at about $37,000 a year.

Isenberg said he knows he does not have the life experience of his older colleagues. He knows that inmates, who officials guess have an average age of 36 in Charles, might try to use his youth to their advantage. But he thinks it would be wrong to exclude 18-year-olds from corrections jobs based on age alone.

"Judge me as an individual, not by my age," he said.

After less than a year and a half on the job, Isenberg already has begun to notice changes in himself. He walks more slowly, constantly looking over his shoulder. At restaurants, he sits facing the door. He tries to keep everything in front of him.

"It's very important not to miss anything," Isenberg said of his work at the jail. "You are in a dangerous situation."

Until 2002, 21 was the minimum hiring age for all correctional officers in Maryland. Effective that year, the Maryland Police and Correctional Training Commissions lowered the age to 18, largely at the request of small jails that were having trouble filling positions.

In 2007, state legislators passed a law raising the minimum hiring age back to 21 at most state-run facilities, though younger guards hired in recent years were permitted to keep their jobs. This year, they tweaked the law so it applied to all such facilities. The new requirement does not apply to people who have been honorably discharged from the military.

Virginia's state prisons, where 18-year-olds can legally work, employ about 80 correctional officers under 21 among a total staff of 8,445, said Larry Traylor, a spokesman for the Virginia Department of Corrections.

Correctional officers at the D.C. jail must also be at least 21, said Beverly Young, a spokeswoman for the corrections department.

In Maryland, corrections officials were strong proponents of restoring the pre-2002 age requirement in state prisons, said Del. Charles Barkley, who sponsored the legislation.

"After visiting a lot of prisons when I realized they were hiring a lot of 18-year-olds, I thought, 'That doesn't seem appropriate,' " he said. "The prisoners are very manipulative."

Barkley said he would not support a similar law for county facilities, in part because prisoners at the state level more often tend to be "hardened criminals."

Although inmates in state facilities can be incarcerated for life, or even be on death row, sentenced inmates in county jails typically serve terms of no more than 18 months. Even so, defendants charged with serious crimes, including rape and murder, are held in county jails as they await trial.

Some corrections directors say they hire young applicants chiefly because they fear that refusing to do so might constitute age discrimination. Alfred McMurray, director of corrections for Prince George's County, Md., said he hires them simply because he cannot legally reject a "clean applicant."

Arthur Wallenstein, director of correction and rehabilitation for Montgomery County, Md., said he opposed lowering the age to 18 in 2002 but has been impressed by young jailers on his payroll.

"Therefore, perhaps, my concerns were not valid, and we learn with time and also the political changes of new legislation," Wallenstein said.

Isenberg, who lives in Leonardtown, Md., has pictures of himself at age 4 standing next to his father, a U.S. Capitol Police officer, and holding a plastic police badge. He said he always wanted a career in law enforcement, and he figured the best path went through the Charles County Detention Center.

On his first day of work, Isenberg toured the detention center, where his new bosses told him what his days would be like -- a test to scare off the weak-willed, he thinks. He wasn't scared, even as the inmates tried to stare him down, he said.

More than a year later, Isenberg still gets looks. "They test all of the officers," Isenberg said of the inmates. "You have to maintain your professionalism. ... It's all a mind game."

When he works the day shift, Isenberg wakes at 5 a.m. He has trouble relating to college-age friends who have yet to enter the work world. And he doesn't really know how he got to that point in his life.

"You have to go from a kid in high school who's used to listening to adults to telling adults what to do," he said. "The jail will make you grow up."